This invention relates generally to electromagnetic actuators and, in particular, electromagnetic actuators for driving blade mechanisms usable for photographic purposes or the like.
A wide variety of mechanical type actuators are known for use in driving blade mechanisms of cameras. U.S. Pat. Nos. 3,781,099; 3,782,255; and 3,942,183 are illustrative of different kinds of mechanically driven shutter arrangements. Many of such types rely upon a stored energy device, in the form of a mechanically tensioned spring, for driving the blades to open or closed conditions. While they function satisfactorily and provide commercially acceptable reliability, nonetheless, they have certain limitations.
For instance, sophisticated shutter mechanisms are of intricate construction and are, therefore, relatively costly and difficult to manufacture. Moreover, with the use of spring mechanisms the performance characteristics are relatively fixed. This is disadvantageous since their performance characteristics cannot be electronically programmable. Aside from this, the spring biased shutters have dynamic performance characteristics which are not as accurate or as reliable as they might otherwise be. Besides the foregoing drawbacks, they tend to be relatively large and somewhat bulky. Further, because of their complicated mechanical nature they are relatively easily susceptible to failure.
Recent efforts have aimed at improving upon such mechanisms. This is not only because of the limitations mentioned above, but also due to the desire to miniaturize cameras.
Some proposals have suggested using electromagnetic actuators for driving shutter blades. Many of these actuators employ annular field coils with magnetic armatures moving into and out of their cores. These too are considered bulky and, therefore, less than ideal for compact shutter applications.
Another approach is described in U.S. Pat. No. 4,024,552 which discloses shutter blades forming an integral part of the electromagnetic actuator itself. Despite a compact arrangement, such an actuator nevertheless relies upon springs for driving the blades to a terminal condition. In fact, a number of electromagnetic shutter mechanisms of this latter kind rely upon springs for driving the blades to at least a particular position. Exemplary are those disclosed in U.S. Pat. Nos. 4,333,722; 4,338,009; and 4,348,092. Moreover, spring mechanisms tend to bias the shutter blades so as to make them dynamically unstable. Therefore, such systems must typically employ latches to keep them in a stable condition.
Proposals have been put forth for springless shutter mechanisms. One is described in commonly-assigned U.S. Pat. No. 3,882,522. Essentially, this patent discloses use of a rotary type stepper motor for driving the shutter blades between open and closed orientations. Rotary stepper motors while being an improvement over the other kinds of conventional motors are still considered somewhat bulky for optimal miniaturization. Commonlyassigned U.S. Pat. No. 4,325,614 shows use of a rotary stepper motor for driving shutter blades. Another proposal is described in commonly-assigned U.S. Pat. No. 4,265,530 issued to the inventor of the instant application. This patent describes a system using not only a linear electromagnetic actuator, but an electro-magnetic clutching mechanism for intermittently transmitting the forces of the actuator to the shutter blades.
A further proposal for a springless type shutter is disclosed generally in U.S. Pat. No. 4,121,235. This patent discloses, however, an electromagnetic shutter mechanism using a pair of solenoids having relatively bulky annular field coils which when energized actuate a pair of shutter blades interconnected through a force transmitting lever.
A significant improvement over the foregoing type of actuator is described in commonly-assigned and copending application Ser. No. 506,787 filed June 22, 1983, by inventor of the instant application.